Folate is a water-soluble B vitamin that occurs naturally in food. Folic acid is a synthetic form of folate. Because of its high stability and bioavailability, folic acid is the form of folate that is used in supplements and added to fortified foods. Folate helps produce and maintain new cells and is, therefore, important during periods of rapid growth such as pregnancy. Neural tube defects (NTD), serious birth defects that occur around 28 days post conception, result in malformations of the brain (anencephaly) and spine (spina bifida). Infants with anencephaly die at birth or soon after and those with spina bifida are often afflicted with varying degrees of paralysis and disability. Over 30 years ago it was first suggested that folic acid taken periconceptionally could reduce a woman’s chance of having an NTD-affected pregnancy.

There is now convincing evidence that folic acid taken prior to and during the first month of pregnancy can reduce a woman’s risk of having an NTD affected pregnancy. No fewer than 15 cross sectional and case-control studies have examined this relationship and nearly all have been supportive. The most convincing evidence comes from three randomized controlled trials and a public health campaign conducted in China. In one study, periconceptional folic acid taken alone (4 mg) or as part of a multi vitamin reduced the risk of NTD by 72% in women with a prior NTD affected pregnancy. In another study of primary NTD prevention there were no cases of NTD in women receiving folic acid (800 µg) as part of a multivitamin supplement and six cases in women receiving a placebo, representing a complete protective effect (Czeizel & Dudas, 1992). In a population based prevention campaign in China, risk of an affected pregnancy was reduced by 80% in women taking 400 µg folic acid in a northern province of China. Although there is now convincing evidence that folate lowers NTD risk we are no closer at saying how folate prevents NTDs. Most women who have an NTD affected pregnancy are not folate deficient. It has been suggested that additional folic acid during the periconceptional period helps overcome some metabolic block in genetically sensitive women.